Which statement describes a square thread?

• A. It is a common screw thread form used in high-load applications.
• B. It has a 29-degree thread angle.
• C. It is primarily used for pipe sealing.
• D. It is a decorative thread for cosmetics.

Answer: (A)

Square threads are a power screw form where the thread flanks are essentially right-angled, giving a near-square profile. This shape creates a large, flat contact area between the screw and nut, so the axial load is carried more evenly and friction remains relatively low compared with many other thread forms. That combination—high load capacity with efficient motion—makes square threads well suited for translating rotation into linear motion in heavy-duty, high-load devices such as leadscrews, jacks, and machine-tool feeds. They’re a common choice in those contexts because they handle strong forces reliably, though they’re harder to manufacture and aren’t as self-locking as some alternatives.

The other statements reflect different thread forms or uses: a 29-degree angle is characteristic of Acme threads, not square; pipe threads are designed for sealing with tapered or parallel profiles rather than a square profile; and decorative or cosmetic threads aren’t used for functional load-bearing motion in machinery.